Implement more make functions, see:
https://www.gnu.org/software/make/manual/html_node/Functions.html#Functions
+Split "flags" strings. eg. Currently there is no way to pass
+$CFLAGS from autoconf into a goalfile.
+
Make re-execs itself if the Makefile (or any include) changes, and
goals should do something similar. See:
https://www.gnu.org/software/make/manual/html_node/Remaking-Makefiles.html